MICRO Chap 3 Classification, MetabolismPresentation Transcript
Principles of Prokaryotic Growth
Robert Koch (1843-1910)
Developed the strategies for cultivating bacteria
Defined growth requirements
First to use agar for semisolid media
Doubling time varies by species and conditions
Growth can be calculated
N t = N 0 x 2 n N t = total cells in a given time N 0 = starting population of cells n = number of cell divisions Assume t = 20 min (3 per hour) 3 x 4 hours = 12 doublings If N 0 = 10 then 10 x 2 12 = 40,960 bacteria
Bacterial Growth in Nature
Bacteria in nature tend to attach to solid surfaces
These bacteria encase themselves in polysaccharide coatings to form communities
Collectively, these communities are referred to as biofilms
Biofilm communities are highly organized
Cellular movement within the biofilm (usually mediated by pili)
Toxic waste sites
Intracellular “warfare” (i.e., competition)
Obtaining a Pure Culture
Isolation of pure cultures is mandatory for studying bacteria
This is usually accomplished using semi-solid media composed with agar
Agar is a polysaccharide obtained from marine algae
It melts at about 95° C and remains liquid to 45° C
Media are made with agar and usually sterilized in an autoclave
Media are cooled to 60° C, then dispensed into Petri dishes or tubes
After cooling, the agar solidifies, providing a semi-solid surface
The streak plate method for obtaining a pure culture
Agar media in Petri dish
Collect a broth culture with a sterile loop
Streak the plate to deposit individual bacteria at sites on the plate
Incubate for 24-48 hr
Single bacterium grows to millions, forming a colony on the plate
Maintaining a Stock Culture
Once a colony is obtained it is considered pure
This colony can be picked and inoculated into another tube or plate ( subculturing ) to provide a stock of the purified culture for short-term use (weeks)
Long-term storage (years)
This purified culture can also be grown in broth and lyophilized (freeze-dried)
It can also be diluted 1:2 in glycerol and frozen at -70° C
Bacterial Growth in Laboratory Conditions
The Growth Curve
Bacteria exhibit distinct kinetic profiles of growth in the laboratory in closed cultures (systems)
These profiles generally are the same, although time-course between species can be different
Bacterial Population Growth Curve
Bacteria absorb nutrients, synthesize enzymes and prepare for cell division
Dry,calloused areas of the skin have few bacteria, whereas moist folds between the toes and fingers support many bacteria and fungi.
Frequent washing of soap and water removes most of the potentially harmful transient microbes harbored in sweat, oil, and other secretions from moist body parts.
Particularly careful to keep patient’s skin and clothing as free of transient microbes as possible
To help prevent personal infections
To avoid transferring pathogens to patients.
Most infections following burns, wounds and surgery from the growth of resident or transient skin microflora in these susceptible areas.
Microflora of the Mouth
Mouth and throat contain many or varied population of microbes
Areas provide moist, warm mucus membranes that furnish excellent conditions for microbial growth.
Bacteria thrive well I particles of food and in the debris of dead epithelial cells around the teeth.
Shelters anaerobic and aerobic microbes due to oral cavity’s peculiar anatomy.
Anaerobic microbes thrive in gum margins, in cervices between the teeth, and in deep folds on the surface of the tonsils.
Most microbes found in mouth are harmless and beneficial like diptheroids, lactobacilli and micrococci.
Streptococci and staphylococci are potentially opportunistic pathogens and are frequently associated with disease.
Some people carry virulent microbes in their nasal passages or throat but do not have the disease associated with them
Ex. Diptheroids, meningitis, pneumonia and TB.
These people are healthy CARRIERS who are resistant to these pathogens but can transmit them to susceptible person.
Poor dental hygiene allows the growth of microbes that cause dental caries, gingivitis, and periodontitis. Bacteria includes Actinomyces, Lactobacillus, Streptococcus, Neisseria and Veillonella.
Many alpha-hemolytic streptococci are indigenous inhabitants of the mouth and oropharynx.
When large numbers of this group is present, antibiotic therapy should be given to destroy these pathogens that may cause “strep throat and its complication (scarlet fever, rheumatic fever, and glomerulonephritis)
Microflora of the Respiratory tract
Lower respiratory tract, below the larynx is sterile (free of microbes)
Mucus membranes and lungs have defense mechanisms that efficiently removes the invaders.
Membranes of URT, include the naso and oropharynx, provide a suitable environment for growth of manny species of Streptococcus, Staphylococcus, Neisseria, Corynebacterium , yeast, and other microbes.
These microbes are opportunist that cause disease to susceptible host.
Presence of staphylococci. Streptococci, Pseudomonas sp , or yeast found in the sputum specimens would indicate either:
An infectious disease of the lungs
Specimen contamination by indigenous microflora of the URT